Vegetable glue



Patented Jan. 7, 1947 VEGETABLE GLUE Gordon G. Pierson, Lansdale, Pa., assignor to Perkins Glue Company, Lansdale, Pa., a corporation of Delaware i No Drawing. Application January 13, 1944,

Serial No. 518,145

8 Claims. (Cl. 106-213) The present invention relates to a novel vegetable glue base and vegetable glue, and more particularly it relates to a glue product comprising a mixture of cassava starch and white potatostarch, which product possesses advantageous properties making it especially applicable for use in the wood-working trade. The present application is a continuation-in-part of my copending application Serial No. 507,722, filed October 26, 1943, which in turn is a continuationin-part of application Serial No. 495,889, filed July 23, 1943.

Heretofore, Various starches have been used or proposed for use in the preparation of vegetable glues for woodworking purposes, including cassava, corn, potato, and sago starch. Such starches have been converted into glue by bursting them, with or without peroxides, copper salts, and other modifying agents, in a solution of caustic soda and water by well known and standard procedures. Starch glues for wood-working purposes must possess certain characteristics in order to be used successfully. For example, they must not carry excessive amounts of water or caustic soda and must have a relatively heavy body in order to prevent excessive penetration. Such heavy-bodied glues must, however, 'flow readily from containers and pipes and must maintain a reasonable degree of stability, as shown by the continued fluidity thereof, over .a period of several hours. In addition, the consistency of the glue must be such that it is easily and smoothly applied from spreader rolls to veneer sheets in a smooth, continuous layer of suitable thickness.

It will be seen from the above that the fluidity of the glue at the time of its preparation andat least for several hours thereafter is an important characteristic. It is known that the fluidity of the glue varies with the water content thereof; the lower the Water content, the less fluid is the glue, However, the use of excessive Water cannot be relied upon to increase the fluidity of the glue, since excessive Water facilitates penetration of the glue too deeply into the wood, thus producing weak or starved joints. Water introduced into the wood by the gluing operation is the principal factor causing warping, checking, staining, slow-setting, molding, and other difliculties commonly known to'the wood-worker.

Furthermore, the manufacturer of plywood considers it necessary or desirable to eliminate from the glued-up wood constructions, before the ar ticle is finally assembled and finished, nearly all of the water which has been added in the gluing operation. This is usually done by means of a dry kiln or by long exposure under normal room atmospheric conditions. For these reasons, the water content of vegetable glues have been kept as low as possible commensurate with the particular requirements of the glue.

In the original patents of Perkins, a procedure was disclosed for the preparation of a glue made from cassava flour with a water ratio of about 2 to 2 parts of water to 1 part of flour. The method which he described to modify raw cassava flour so that the glue made from it would have a suitable consistency and working characteristics with as little as 2 parts of water was laborious and expensive. Subsequently, Pierson in Patent No. 2,030,073 described a more simple process of modifying cassava flour, involving the use of a copper salt. By this process, a glue having excellent workability and consistency from cassava flour using no more than 2 to 2 parts of water for each part of glue base was economi cally obtained. Since the grant of these patents, it has been established that glue to be satisfactory for general wood-working purposes should not carry more than 2 parts of water and should show a viscosity of about 45,000 to 50,000 centipoises, determined according to the method described in Patent No. 2,030,073.

Heretoiore, the vegetable glues which have been sold for use in the manufacture of the better grades of plywood and furniture have generally been made from cassava flour, since that starch possesses properties, not associated with other starches, making it especially adapted for the preparation of such glues. For this reason, the trade has developed machinery and working habits based on the properties of a vegetable glue made from cassava starch, and the attempts to .use other sources of starch have not only failed to provide a product with the desired properties of a glue made from cassava starch, but the production of such a glue has presented diiiiculties due to the fact that the standardized machinery and methods of the trade are inapplicable thereto.

White potato flour although a domestic product available at reasonable prices and in large quantities has never been accepted as a material suitable for use in the preparation of a vegetable glue of the better grade. Raw potato starch when burst without the use of modifying agent requires about 3 parts of water to 1 part of starch to get a sufficiently low viscosity. If the raw potato starch is modified by the methods described in the Perkins patents, the water ratio can be reduced somewhat, but auseable and practical consistency cannot be'obtained. If it is modified by the method of Patent No. 2,030,073, the water ratio can be reduced, but not enough for the best results. also presents another problem because, in the conversion of the starch into glue, the mass The use of potato starch be thrown from the pulleys, due to the extreme toughness of the mixture in the kettle at this stage.

One object of the present invention is to provide a vegetable glue base, having white potato flour as a substantial ingredient thereof, which is convertible into a glue having the characteristics which are necessary for a successful vegetable glue in the wood-working trade.

Another object of the invention is to provide a vegetable glue base comprising a mixture of white potato starch and cassava starch, which not only may be easily converted into a vegetable glue in the machinery and by the procedure now used in the production of vegetable glue from cassava starch alone but which may be converted into a glue of desirable properties with less strain on the mixing equipment than has been the case with any vegetable glue heretofore manufactured.

A further object of the invention is to provide a vegetable glue comprising a mixture of white potato flour and cassava starch which furnishes a better bond in the manufacture of plywood and the like than can be obtained from glues prepared from cassava starch alone at the same water ratio and having substantially the same viscosity.

Other objects will be apparent from a consideration of this specification and the claims.

While the present invention will be described with particular reference to a glue for the woodworking trade, it is to be understood that the glue of the invention may be used for any purpose where a glue of the properties described is desired.

The vegetable glue base of the present invention comprises substantial proportions of both cassava starch and white potato starch. The ratio of the two starches may be varied over a wide range depending upon the particular properties desired in the vegetable glue, the ratio of the cassava starch to white potato starch being between about 7 to 3 and about 3 to 7 and a very satisfactory glue is obtained when there are present substantially equal parts of cassava starch and white potato starch. Generally, however, the ratio of cassava starch to white potato starch will be present between about 4 to 6 and 6 to 4. It is to be understood that small amounts of other starches such as corn, wheat or rye starch, for example up to about 10% may be included without deleteriously affecting the properties of the glue product.

In preparing the glue, the mixture of starches as a glue base or the individual starches may be converted in a glue-making kettle into a glue by subjection to heat in an aqueous solution of caustic alkali. This treatment causes the starch grains to burst and to form a glue of the required consistency. Due to the availability of caustic soda, this chemical will usually be employed, but caustic potash can be employed if desired. Generally, the amount of caustic soda employed will be between about 1 to 1.5% and 5% based on the total starch content, the use of about 3% being preferred. The ratio of water to starch will advantageously be maintained at minimum in any particular case, but water in excess thereof may be present. As will hereinafter appear, a copper salt and/or a calcium compound is preferably present during the conversion of the starches into glue in which case the water content can be lowered. Either or both of these compounds may be added to the mixture of potato and cassava starch to form components of the glue base or may be added to the kettle. If desired, a peroxide or other modifying agent may also be present in the vegetable glue base or such material may be added to the glue-making kettle at the time of the conversion. In order to produce a glue satisfactory for general use and also having the optimum desirable characteristics recited in Patent No. 2,030,073, parts of the glue base is mixed with the required amount of water and 3 parts of caustic soda dissolved in a small amount of water are added. This mixture is then heated with agitation to a temperature of about 150 F., after which, it is agitated and cooled to room temperature.

As stated, the glue of the present invention can be prepared in the usual glue-making equipment and by the usual procedures employed in the production of glues from cassava starch. In preparing the glue, for example using about 3% of caustic soda, the potato starch upon conversion into glue passes through a tough rubbery stage due to the swelling and bursting of the starch grains at a temperature of from about F.

to F. after which the mass becomes thinner ture is reached and the cassava starch bursts at a higher temperature, the total glue mass of the present invention which comprises substantial amounts of both cassava starch and white potato starch is converted with less strain on the mixing equipment thana glue made from the individual starches and in fact is converted with less strain on the equipment than any vegetable glue previously known. Furthermore, as pointed out in the object of the invention, the preferred embodiment of the glue of the present invention possesses all of the characteristics which are required in a successful vegetable glue in the woodworking trade, and in addition a better bond is provided than can be obtained by the use of glues made of cassava starch alone.

In order to reduce the water content required in the glue, it is desirable to have present, at the time of the production of the glue, a small amount of a copper salt as disclosed and claimed in Patent No. 2,030,073 or a small amount of a calcium compound furnishing calcium ions in the presence of water and possessing the property of liquefying and stabilizing the glue made from said base, as described and claimed in my copending application Serial No. 507,722, filed October 26, 1943.

Advantageously, smallamounts ofboth the copper salt and the calcium compound are present.

Examples of the copper salt are copper sulphate, copper nitrate, and copper chloride, and the amount employed need be only a fraction of a per cent., for example from 01% to 0.1%, and generally not more than 0.2%, based on the total weight of the starch. While larger amounts may be added, the use thereof is not recommended since with larger quantities the glue takes on an unpleasant green color and because larger quantities tend to produce a lumpy consistency of the glue which is undesirable.

The calcium compound, as previously stated, is sufficiently soluble to provide a significant amount of calcium ions when mixed with water and possesses the property of liquefying and stabilizing the starch glue when the starch is burst in the presence of caustic alkali and water. The term liquefying refers to the ability of the calcium compound to bring about a reduction in the viscosity or water-absorptive capacity of the glue; and the term stabilizing refers to the ability of the calcium compound to prevent or retard the thickening action of the glue. The calcium compound is preferably finely divided and may be the hydroxide, peroxide, or oxide, or a salt of an organic or inorganic acid, such as the acetate, chloride, nitrate, iodide, bromide, ferrocyanide, hypochlorite, citrate, formate, lactate, and the like. It is to be understood that the compounds named are merely illustrative, and that any other calcium compound possessing the properties stated may be employed. If a calcium salt is employed, the anion of the salt is relatively unimportant so long as it does not possess a coagulating effect which would counteract the desired liquefying and stabilizing effects. Of the various calcium compounds available for use, calcium hydroxide is preferred. When a peroxide is to be employed, calcium peroxide may be used to provide all or a portion of the calcium ions and of the oxidizing action. When a calcium salt is employed, the use of a nonhydroscopic'salt is recommended. If a peroxide is employed, a calcium salt will advantageously be selected which does not destroy the beneficial effects of the peroxide.

The calcium compound is present in amounts sufiicient to liquefy and stabilize the starch and the amount employed is below that which will exert a thickening or coagulating effect on the starch. In general, the calcium compound is present in a small amount based on the total weight of the starch content, for example, from about 0.1% to about 1.0% calculated as Ca(OH) 2, about 0.3% to 0.5% being preferred. In the case of the use of a finely divided, active calcium hydrate, the amount employed will usually not exceed 0.8%. When a calcium salt is employed, the actual amount employed may, of course, be correspondingly higher, but for convenience, the figures have been given on the amount of calcium compound calculated as Ca(OI-I)z by weight based on the total weight of the starch content.

Referring further to the ratio of water to the solid content of the glue, it may, as pointed out, be greater than the minimum but due to the objections referred to in using :more water than is required, the amount of water is advantageously kept at a minimum. In the case of glue in which neither a copper salt nor a calcium compound has been used, the ratio of water to the solid content of the glue is generally between about 2% to 1 and 2% to 1. When a copper salt or a calcium compound is employed, the water ratio may be between about 2% to l and 2 toy I. In the case of the use of both the copper salt and the calcium compound, the water ratio may be between about119 to 1 and 2 to 1.

The following examples are illustrative of the invention:

Example I Cassava Potato 40 Water 240 Caustic 3 Example II Cassava 40 Potato 60 Water 250 Caustic 3 Example III Cassava 50 Potato 49.97 Copper sulphate .03 Water 212 Caustic 3 Example IV Cassava 50 Potato 49.7 Hydrated lime .3 Water 212 Caustic 3 Example V Cassava 50 Potato 49.67 Copper sulphate .03 Hydrated lime .3 Water 200 Caustic 3 Considerable modification is possible in the amounts of materials employed in preparing the glue base and glue, as well as in the steps of making the vegetable glue, without departing from the essential features of the invention.

I claim:

1. A vegetable glue comprising the products of reaction of cassava starch and white potato starch in a ratio of between about 7 to 3 and 3 v to 7, caustic alkali and water, the water being present in an amount to provide a ratio of water to starch not greater than about 2% to 1.

2. The product of claim 1 wherein the cassava starch and potato starch are present in a ratio of between about 6 to 4 and 4 to 6, wherein the caustic alkali is caustic soda and is present at the time of the reaction in an amount between about 1.5% and 5% based on the total weight of the starch.

3. A vegetable glue comprising the products of reaction of cassava starch and white potato starch in a ratio of between about 7 to 3 and. 3 to *l, caustic alkali, a calcium compound furnishing calcium ions possessing the property of liquefying and stabilizing the glue in an amount between about 0.1% and about 1.0%, and water, the water being present in an amount to provide a ratio of water to starch not greater than about 2 to 1.

4. The product of claim 3 wherein the cassava starch and potato starch are present in a ratio of between about 6 to 4 and 4 to 6, wherein the caustic alkali is caustic soda and is present at the time of the reaction in an amount between 7 about 1.5% and 5% based on the total weight ofthe starch.

5. A vegetable glue comprising the products of reaction of cassava starch and white potato starch in a ratio of between about 7 to 3 and 3 to 7, caustic alkali, a calcium compound furnishing calcium ions possessing the property of liquefying and stabilizing the glue in an amount between about 0.1% and about 1.0%, a small amount of a copper salt, and water, the water being present in an amount to provide a ratio of water to starch not greater than about 2% to 1.

6. The product of claim 5 wherein the cassava starch and potato starch are present in a ratio of between about 6 to 4 and 4 to 6, wherein the caustic alkali is caustic soda and is present at the time of the reaction in amount between about 1.5% and 5% based on the total weight of the starch.

7. A vegetable glue comprising the products of reaction of cassava starch and white potato starch in a ratio of between about 7 to 3 and 3 to 7, caustic alkali, a small amount of a copper salt, and water, the water being present in an amount to provide a ratio of water to starch not greater than about 2% to 1.

8. The product of claim 7 wherein the cassava starch and potato starch are present in a ratio of between about 6 to 4 and 4 to 6, wherein the caustic alkali is caustic soda and is present at the time of the reaction in an amount between about 1.5% and 5% based on the total weight of the starch.

GORDON G. PIERSON. 

